This invention concerns a nozzle assembly, a fuel injector including such an assembly and an internal combustion engine comprising such an injector.
In the field of fuel injection for internal combustion engines, new developments are largely driven by new coming emission regulations, as well as noise and fuel consumption targets. A potential way to improve combustion is to start fuel injection long before the piston reaches its top dead end position (TDC). In some instances, some fuel can be injected up to 180° before TDC. For such an early injection, the spray angle should be small in order to avoid spraying fuel on the cylinder walls, since this would have major drawbacks on emissions, oil dilution and cylinder liners wear. On the contrary, when injection takes place just for TDC, the spray angle should be large in order to suit diesel piston bowls. In order to obtain two spray angles, some nozzles are provided with telescopic needles adapted to feed of two rows of holes or outlets.
In FR-A-2 854 661, a telescopic needle allows a double stage injection with a first spray having a narrow angle and then a mixture of two sprays. In U.S. Pat. No. B-6,557,776, another telescopic needle is used to obtain a first spray through a first row of holes, for small quantities of fuel, and a second spray through two series of holes available, for the main injection. In these systems, the second spray includes a flow corresponding to the first spray. In other words, the second spray is a combination of the first spray and another spray, because prior art systems do not allow the selection of two different rows of holes or orifices. It is only possible to inject fuel either with the first row of holes or with both rows of holes, but not with the second row of holes alone. Moreover, the prior art devices imply complex designs with several actuators, which decreases the reliability of these systems and increases their costs.
U.S. Pat. No. B-6,769,635 discloses a fuel injector whose nozzle assembly includes two rows of holes which can be fed independently from each other thanks to two electrical actuators powered and driven according to the needs. This fuel injector is quite complex to manufacture, expensive and difficult to set.
It is desirable to provide a nozzle assembly which allows to obtain two different spray geometries thanks to two sets of orifices used independently from each other, without needing complex and expensive valves to define which type of orifices is used for spraying fuel within a combustion chamber.
With this respect, the invention concerns a nozzle assembly for injecting fuel into a combustion chamber of an engine, this assembly comprising a first needle and a second needle controlling respectively fuel flow towards a first series of outlets and a second series of outlets. This nozzle includes a passive control valve adapted to select, on the basis of the fuel feeding pressure, the needle to be activated for fuel delivery to the combustion chamber.
Thanks to an aspect of the invention, the passive control valve enables to select which flow path can be open and which series of outlets can be fed when fuel is to be delivered to the combustion chamber.
According to advantageous aspects of the invention, such a nozzle assembly may incorporate one or several of the following features:                the passive control valve is driven with fuel coming from a source of fuel under pressure and controls flow of fuel coming from two back-pressure chambers acting on the needles.        the passive control valve is adapted to selectively connect, depending on the pressure level of the driving fuel coming from the source of fuel under pressure, either of the back-pressure chambers with a discharge line.        the assembly includes a solenoid valve adapted to pilot one of the needle, depending on the selection made by the passive control valve.        the solenoid valve controls the connection between the discharge line and a low pressure circuit.        two fuel paths are defined between a source of fuel under pressure and the passive control valve, each path including a back-pressure chamber acting on one of the needles.        each fluid path includes at least two throttles located respectively upstream and downstream of the corresponding back-pressure chamber.        the throttles are made in at least a part mounted on a body of said assembly which surrounds the needles.        one throttle is located between the source of fuel under pressure and each back-pressure chamber.        a dedicated throttle is located on the entry line of each back-pressure chamber.        a throttle is located on a feeding line common to both back-pressure chambers.        one throttle is located between each back-pressure chamber and the passive control valve.        one throttle is located downstream of the passive control valve.        the outlets series include a first series of outlets distributed around a central axis with a frustroconical configuration having a first angle and a second series of outlets coaxial with the first series, with a frustroconical configuration having a second angle whose value is superior to the value of the first angle.        the assembly comprises two back-pressure chambers, each back-pressure chamber acting on one needle.        the back-pressure chambers and the needles are coaxial.        the passive control valve comprises a valve core movable in translation within a valve body and subject, on one side, to the action of the fuel feeding pressure and, on the other hand, to the action of elastic return means.        
An aspect of the invention also concerns a fuel injector comprising a nozzle assembly as mentioned here-above. Such a nozzle assembly is more flexible to provide fuel to a combustion chamber.
Finally, an aspect of the invention also concerns an internal combustion engine comprising at least a cylinder provided with a fuel injector as mentioned here-above. Such an engine offers more possibilities for performance development and opens the door to further potential improvements.